Method of manufacturing a preform for asymmetrical optical fiber

Abstract

Disclosed is a method of manufacturing a preform for an asymmetric optical fiber which comprises the steps of (a) fixing plural transparent glass rods involving at least one core-mother rod functioning as the core in said optical fiber in parallel relationship, (b) depositing glass soot around an assembly of said plural parallel fixed glass rods, thereby providing a single porous cladding bearing the predetermined shape, and (c) vitrifying the porous cladding by thermal fusion, thereby providing the entirely integral transparent preform. The above method does not involve any process of perforating a drilled-pore which is needed inevitably in conventional method. Therefore, it is possible to obtain a long preform with high dimensional precision, and to fabricate the optical fiber with low transmission loss.

What is claimed is: 
     
       1. A method of manufacturing a preform for an asymmetrical optical fiber which comprises the steps of: (a) fixing and assembling a plurality of transparent glass rods in parallel relationship and spaced from each other in a pair of disk-shaped jigs, each of said jigs having a plurality of openings to securely hold said plurality of transparent glass rods in said spaced apart and parallel relationship, to form a rod assembly, and said plurality of glass rods including at least one core-mother rod functioning as a core in said optical fiber;   (b) depositing glass soot around said rod assembly of said plurality of fixed glass rods by rotating said rod assembly and spraying the glass soot on said rod assembly while it is being rotated, thereby forming a single porous glass cladding which surrounds all of the glass rods and which has a predetermined shape; and   (c) removing said pair of jigs from said transparent glass rods and vitrifying said porous glass cladding to a single transparent cladding by thermal fusion, thereby forming an entire integral transparent preform which can be drawn into an asymmetrical optical fiber, said transparent cladding having a smaller refractive index than said at least one core-mother rod.   
     
     
       2. The method of claim 1, comprising fixing and assembling only one core-mother rod functioning as said core in said optical fiber, and two stress-applying-mother rods functioning as stress-applying parts in said optical fiber. 
     
     
       3. The method of claim 1, comprising fixing and assembling two core-mother rods functioning as said core in said optical fiber. 
     
     
       4. The method of claim 1, comprising controllably rotating said rod assembly during said spraying of said glass soot so as to cause said porous glass cladding to have a predetermined cross sectional shape. 
     
     
       5. The method of claim 4, comprising controllably rotating said rod assembly during said spraying of said glass soot so as to cause said porous glass cladding to have a substantially circular cross sectional shape. 
     
     
       6. The method of claim 4, comprising rotating said rod assembly during said spraying of said glass soot so as to cause said porous glass cladding to have a substantially elliptical cross sectional shape. 
     
     
       7. The method of claim 1, wherein said step of removing said paired jigs from said transparent glass rods is carried out before carrying out said vitrifying step. 
     
     
       8. The method of claim 7, wherein at least one of said glass rods extends from said porous cladding and wherein said vitrifying step is conducted by suspending vertically said rod assembly with said porous cladding thereon in a heating furnace by means of a wire connected to an upper end portion of said at least one glass rods extending from said porous cladding, and by moving the rod assembly downward to pass through a vitrifying heating zone provided in the heating furnace. 
     
     
       9. The method of claim 1, further comprising the step of thermally dehydrating said porous glass cladding by applying a dehydrant. 
     
     
       10. The method of claim 1, wherein said core-mother rod comprises a core portion and core rod cladding portion surrounding said core portion. 
     
     
       11. The method of claim 10, wherein said core rod cladding portion has a thickness of about 4 times the diameter of said core portion.